1. Field of the Invention
The present invention relates generally to a method of capping the exposed surface of a mass of particulate materials that tend to become airborne or unconsolidated due to environmental factors such as wind and rain.
2. Description of the Prior Art
There are a variety of circumstances in which environmental and economic concerns require enclosing the exposed surfaces of a mass of particulate materials. These surfaces include stockpiles of dust producing bulk materials as well as bare and unconsolidated land masses. Capping readily forms a barrier that encloses these exposed surfaces to prevent their loss due to environmental factors.
For instance, capping mining and industrial tailings ponds would reduce dusting and pollution caused by the ponds. In areas with previous or present mining operations, thousands of acres of tailings ponds are subjected to high winds which cause "dusting" and the creation of intolerable dust storms. These ponds are made from finely ground waste ore that was previously incorporated into a liquid slurry, pumped to a dammed land area and allowed to settle and dry. In the case of active mining operations, aqueous fines-containing effluent is pumped to the tailings pond, where the water collects and clears. The cleared water is then pumped back to the mining operation. Part of these large pond areas are allowed to dry up, so that tailings remain at a constant level. Winds easily blow the dried up fines, thus "dusting" the communities downwind.
Due to increasing population pressures, many of these sites lie near inhabited areas. Especially in the Western United States, expanding environmental regulations and political pressure make it imperative that an economical solution to the tailings ponds problem is found to prevent dusting and reduce airborne pollution. Capping these areas would be beneficial.
Other industrial processing sites would benefit from capping. For example, ponds with fines-containing aqueous effluent, sludges and slimes, such as those from the phosphate industry, tar sands industry or bauxite industry, continue to pollute the environment despite efforts to control the pollution. The borax industry, another example, has high levels of arsenic in its waste dumps. Capping these waste dumps would prevent dusting, and thus contain the arsenic within the dump. Manufacturing and power generating industries, such as power plants, sugar mills and the like, generate storage piles which can also benefit from capping. These industries stockpile large amounts of fine particulate waste or process materials at any given location. Capping these open stockpiles can prevent dusting and erosion.
The above-mentioned industries are not the only industries where capping would be beneficial. Sanitary landfills frequently leave exposed areas of debris as operators move around the landfill site. Capping such areas would prevent blowing debris as well as allow daily cell closure for odor and vector control. In many areas, hazardous landfills are presently required to be routinely capped. Since many of these hazardous materials are acidic, capping to prevent blowing dust as well as stabilize pH improves the efficiency of hazardous landfill operations.
Capping would be useful in the construction industry. Construction sites frequently store large piles of dirt and top soil during construction. Wind often causes excessive dusting and loss of topsoil. Depending on the site and location, the berms of many roadsides or ditches are frequently built with loose material that generates dust through the swirling effect of moving vehicles passing by them on the road. Such exposed areas can be advantageously treated by capping.
The capping material can help revegetate bare exposed areas, such as reforesting after forest fires, seeding grass after construction, and the like. The capping material could serve as an overlay over seeded land or modified to include grass or tree seeds within the material. The capping material would provide a convenient medium for the reseeding of the affected area while protecting the top soil, thus providing both erosion control and revegetation.
A significant amount of bulk materials, such as coal, fly ash, ore and the like, are stored and/or transported in open containers, such as rail cars or trucks. Open rail coal cars travelling from the Western to Eastern United States frequently lose between 2% to 5% by weight of their load through dust emissions. Such dust emissions increase with wind erosion and the vibration of the rail car during transit. Capping would reduce this loss.
Prior to capping, additives were generally applied to an exposed surface of the bulk material in the form of a liquid spray or foam. U.S. Pat. No. 4,836,945, issued Jun. 6, 1989, to Kestner contains a detailed discussion of various prior art chemical controls including the use of water and oil sprays. Included among the prior art materials are aqueous solutions of vinyl esters, latex emulsions, asphalts, waxes and various other polymers. These prior art formulations tend to be expensive and, in some cases, use environmentally objectionable components.
U.S. Pat. No.5,118,219, entitled "Method of Capping Tailings Ponds", issued Jun. 2, 1992, to Daniel D. Walker, Jr. teaches a method for capping tailings ponds. A mineral formulation is prepared by mixing together lime, a pozzolanic component, a sulfur component and water. The mineral formulation is applied to the surface of the fines-containing tailings pond and is allowed to harden to form a surface coating on the tailings pond. A thin, semi-permeable cap forms that resists weathering.
However, field tests of the above-mentioned method showed room for improvement. Capping tailings ponds with the '219 formulation was ineffective in areas exposed to constant winds. The capping materials blew away within a few days under constant winds.
The present invention is an improvement upon the previous '219 formulation, providing a method especially well adapted for capping exposed areas and preventing fine particles and debris from blowing in the wind. The present invention provides an environmentally acceptable, semi-permeable, cementiceous, non-hazardous, membrane to cap exposed land areas, including areas with deposited particulate materials.
Another object of the invention is to provide a mineral formulation for capping land areas that serves as a suitable matrix for carrying and depositing plant and vegetable seeds during reseeding and revegetation operations.
Another object of the invention is to provide a semi-permanent cap for surface land areas that is semi-permeable and allows water to pass through without breaking the integrity of the surface.
Another object of the invention is to provide a capping formulation for land areas which can be colored to match its surroundings.